This invention relates generally to an apparatus for weighing objects, and more particularly, to a weighing cell having protection from overload forces applied to the scale's platform and rapid vibrational damping to reduce the time that an accurate readout is produced after a load is placed thereon.
In weighing cells, such as the type commonly used to weigh articles for determining postage, it is desirable to provide protection against the cell being overloaded, particularly by shock loads. Such overloading tends to force the cell out of calibration. U.S. Pat. No. 4,107,985 discloses one approach to this problem. A parallelogram structure is utilized to make the load cell insensitive to, and unaffected by, off-center loading. In this type of structure, the bending moment produced by non-axial loading is transmitted to restraining arms in the load cell rather than through the force measuring element, of sensing beam. Axial over-loading, on the other hand, is prevented by the mechanical interfacing of the load cell and its base which is separated at a partial gap therefrom.
More recently, load cells of high accuracy and low cost have been made available for application to weighing cells. These devices, called single-point load cells, generally have safe overload margins in excess of their rated capacities and give accurate weighing of objects regardless of where the object is placed on the platform. With the commercial introduction of these newer load cell designs, it is possible to replace the complicated parallelogram structures formerly used in weighing cells with more economical structures which concentrate on shock overload protection and the lessening of vibrational damping time.
U.S. Pat. No. 4,181,001 discloses a representative single point load cell. The device disclosed in this patent is primarily directed to eliminating the effects of internal axial forces, such as those produced by machining, fabrication stresses or temperature gradients, on the sensing beam. It seeks to provide better accuracy and linearity, as well as off-center load capabilities. This structure isolated the sensing beam from all extraneous forces through the configuration of the load cell itself. Only the axial forces placed on the load cell find their way to the sensing beam. All other forces are funneled away form the sensing beam and to another member within the parallelogram structure.
Accordingly, it is a primary object of the present invention to improve weighing cell by providing shock overload protection.
It is another object of the present invention to lessen the time to dampen vibrations produced when an object is placed on the platform of the weighing cell.
It is another object of the present invention to improve axial overload protection in weighing cells.
It is another object of the present invention to improve non-axial overload protection in weighing cells.